The Synthesis of Some Pyrrolidines as Potential Precursors to Retronecine

Methyl beta-D-galactopyranoside was converted into methyl 4-azido-3-O-benzyl-6-O-t-butyldi-phenylsilyl-2,4-dideoxy-beta-D-arabino-hexoside, but subsequent transformation of the anomeric centre into a dithioacetal was unsatisfactory. Alternatively, methyl beta-D-galactopyranoside easily gave methyl 4-azido-3,6-di-O-benzyl-2,4-dideoxy-beta-D-arabino-hexoside, and this could be transformed by a reductive amination into two pyrrolidines as potential precursors to retronecine. Related chemistry gave (4S,5S,6R)-6-benzyloxy-4-benzyloxymethyl-3-oxa-1-azabicyclo[3.3.0]octan-2-one, the structure of which was confirmed by a single-crystal X-ray structure determination. Finally, the synthesis of a potential precursor to heliotridine (an epimer of retronecine), namely methyl 4-azido-3-O-benzyl-6-O-t-butyldiphenylsilyl-2,4-dideoxy-alpha-D-ribo-hexoside, from methyl alpha-D-mannopyranoside is reported.